Advanced control strategies for high-temperature heat pumps: a review

High-temperature heat pumps (HTHPs), capable of delivering heat at sink temperatures above 80 °C, are emerging as an important technology for industrial decarbonisation and energy efficiency, offering a low-carbon alternative to conventional fossil-fuel-based heating systems. However, their wider deployment remains limited by challenges related to performance optimisation, dynamic operation, and effective integration with renewable energy sources. These challenges are particularly pronounced because HTHPs operate under high temperature lift and pressure ratios, often close to thermodynamic, material, and safety limits, making system performance and reliability highly sensitive to control strategies. While existing reviews of HTHPs have primarily addressed thermodynamic cycle design, working fluid selection, and component development, the role of control in enabling safe and efficient HTHP operation has received comparatively little systematic attention. This review addresses this gap by providing the first comprehensive, control-oriented survey of HTHPs, with three explicit objectives: (i) to systematically categorise and evaluate existing control methodologies across the full spectrum from classical to AI-based approaches; (ii) to identify persistent research gaps in standardisation, multi-objective optimisation, real-time deployment, and grid integration; and (iii) to propose prioritised future research directions to accelerate the reliable industrial deployment of HTHPs. It covers a broad range of control approaches, including classical control methods, model-based control, robust control, and data-driven and artificial-intelligence-based techniques. Particular attention is given to how control systems can manage high-temperature-specific constraints, such as compressor discharge temperature limits, pressure boundaries, and component protection, while maintaining high efficiency, stable operation, and flexibility under varying load and source conditions. The paper highlights the importance of advanced control architectures in enabling safe, efficient, and flexible operation of HTHPs in industrial energy systems. It also identifies key research gaps and outlines future research directions, providing a structured and control-oriented perspective to support the reliable and large-scale deployment of high-temperature heat pumps in low-carbon industrial applications.